A. Field of the Invention
The present invention relates generally to impact or jarring tools, and more particularly, to a fluid operated jarring tool for use in well bores that jars upwardly when the tool is in tension and downwardly when the tool is in compression.
B. Description of the Prior Art
In downhole well operations, there is a need for jarring or impact devices. For example, in workover operations using coiled tubing or snubbing equipment, it is necessary to provide downward jarring impact at the bottom of the string to enable the string to pass obstructions or otherwise enter the well. During fishing operations or other operations, such as paraffin scraping, it is sometimes necessary to apply upward jarring or impact forces at the bottom of the string if the fishing tool or the like becomes stuck.
In my prior U.S. Pat. No. 3,946,819, I disclose a fluid operated well tool adapted to deliver downward jarring forces when the tool encounters obstructions. The tool of my prior U.S. Pat. No. 3,946,819, generally includes a housing with a tubular stem member telescopically received in the housing for relative reciprocal movement between a first terminal position and a second terminal position in response to fluid pressure in the housing. The lower portion of the housing is formed to define a downwardly facing hammer and the stem member includes an upwardly facing anvil which is positioned to be struck by the hammer. The tool includes a valve assembly that is responsive to predetermined movement of the stem member toward the second terminal position to relieve fluid pressure and permit the stem member to return to the first terminal position. When the valve assembly relieves fluid pressure, the hammer moves into abrupt striking contact with the anvil. The tool of my prior U.S. Pat. No. 3,946,819, is very effective in providing downward repetitive blows. However, the tool of my prior patent will not produce upwardly directed blows.
In U.S. Pat. No. 3,361,220, there is disclosed a jarring or drilling mechanism that may be adapted to provide upward or downward, or upward and downward blows. The mechanism of the '220 patent includes a housing having opposed axially spaced apart anvil surfaces and an impact element or hammer having opposed axially spaced apart hammer surfaces slidingly mounted within the housing between the anvil surfaces. A spring is provided for urging the hammer upwardly. When it is desired to use the mechanism of the '220 patent for jarring, a valve including a closure and a compression spring is dropped down the string to the mechanism.
In general, the mechanism of the '220 patent operates by fluid pressure acting on the valve and hammer to urge the valve and hammer axially downwardly until the downward movement of the valve is stopped, preferably by the full compression of the valve spring. When the downward movement of the valve stops, the seal between the valve and the hammer is broken and the valve moves axially upwardly.
The direction of jarring of the mechanism of the '220 patent is determined by the relationship between the fluid pressure and the strength of the spring that urges the hammer upwardly. Normally, the mechanism is adapted for upward jarring. When the valve opens, the hammer moves upwardly to strike the downwardly facing anvil surface of the housing. The mechanism can be made to deliver a downward and upward blow by increasing the fluid pressure and decreasing the strength of the spring that urges the hammer upwardly. When the mechanism is so arranged, the downward momentum of the hammer is increased such that the hammer strikes the upwardly facing anvil of the housing prior to being urged upwardly to strike the downwardly facing anvil surface. The mechanism of the '220 patent can be adapted to produce only downward forces by either shortening the length of the valve spring or by lengthening the valve such that the valve recloses prior to the hammers reaching the downwardly facing anvil surface on the upstroke.
A primary shortcoming of the mechanism of the '220 patent is in its inability to provide bidirectional impacts without modifying the mechanism. A further shortcoming of the mechanism of the '220 patent is in its inability to provide either an upward jarring force or a downward jarring force depending upon the wishes of the operator when the mechanism is downhole. Yet a further shortcoming of the mechanism of the '220 patent is in its rather limited effectiveness in producing downward impacts, in that the downward force on the hammers is provided solely by its momentum, which is opposed by both fluid pressure and the spring urging the hammer upwardly.
It is therefore an object of the present invention to provide an apparatus which overcomes the shortcomings of the prior art. More particularly, it is an object of the present invention to provide a bidirectional fluid operated jarring apparatus that produces strong jarring forces in either the upward or downward direction. It is a further object of the present invention to provide a jarring apparatus that can be used to provide upward or downward impact forces as desired downhole without modifying the tool. It is a further object of the present invention to provide an apparatus that provides downward jarring forces when the tool is in compression, as when the tool is being run downwardly, and which produces strong upward forces when the tool is in tension, as when the tool is being pulled upwardly.